The present invention relates to a semiconductor light-emitting device having a current diffusion layer and method for manufacture thereof.
In recent years, LEDs (Light-Emitting Diodes), which are semiconductor light-emitting devices, have been in the limelight as indoor/outdoor display devices. In particular, with their trend toward higher brightness, the outdoor display market has been rapidly expanding while LEDs have been growing as a medium to replace neon signs. High-brightness LEDs of visible range in such fields have been developed by AlGaInP-based DH (Double Hetero) type LEDs. FIGS. 25A, 25B, 25C show a top view, a sectional view and a functional view, respectively, of a yellow-band AlGaInP-based LED as a semiconductor light-emitting device.
In this semiconductor light-emitting device, as shown in FIGS. 25A and 25B, an n-GaAs buffer layer 301 (thickness: 0.5 μm, Si doping: 5×1017 cm−3), an n-AlGaInP cladding layer 302 (thickness: 1.0 μm, Si doping: 5×1017 cm−3) an undoped (Al0.3Ga0.7)0.5In0.5P active layer 303 (thickness: 0.6 μm), a p-AlGaInP cladding layer 304 (thickness: 0.7 μm, Zn doping: 5×1017 cm−3), a p-AlGaAs current diffusion layer 305 (thickness: 6 μm, Zn doping: 3×1018 cm−3), and a p-GaAs cap layer 306 (thickness: 0.1 μm, Zn doping: 3×1018 cm−3) are grown on an n-GaAs substrate 310 by MOCVD process, and a first electrode 311 is formed on the substrate side while a second electrode 312 is formed on the grown layer side. Regions of the p-GaAs cap layer 306 other than a device center region thereof opposed to the grown-layer side second electrode 312 have been removed. In this semiconductor light-emitting device, having a pn junction formed within the active layer 303, light emission is generated by recombination of electrons and holes. With this semiconductor light-emitting device molded into 5 mm dia. resin, when a 20 mA current was passed therethrough, the resultant emission intensity was 1.5 cd.
In this semiconductor light-emitting device, as shown in FIG. 25C, a current injected from the grown-layer side second electrode 312 expands within the p-AlGaAs current diffusion layer 305, being injected into the active layer 303, where most part of the current flows to the region under the second electrode 312. As a result, light emission over the region under the second electrode 312 is intercepted by the second electrode 312 so as not to go outside, resulting in an ineffective current. This leads to a problem that the emission intensity would be lower.
Thus, as an solution to this problem, there has been proposed a structure in which a current blocking layer for blocking the current is introduced under the second electrode 312.
FIGS. 26A-26C show a top view, a sectional view and a functional view, respectively, of a semiconductor light-emitting device having the structure in which the current blocking layer is introduced. In this semiconductor light-emitting device, as shown in FIGS. 26A and 26B, an n-GaAs buffer layer 321 (thickness: 0.5 μm, Si doping: 5×1017 cm−3), an n-AlGaInP cladding layer 322 (thickness: 1.0 μm, Si doping: 5×1017 cm−3), an undoped (Al0.3Ga0.7)0.5In0.5P active layer 323 (thickness: 0.6 μm), a p-AlGaInP cladding layer 324 (thickness: 0.7 μm, Zn doping: 5×1017 cm−3), a p-AlGaInP intermediate band gap layer 325 (thickness: 0.15 μm, Zn doping: 2×1018 cm−3), a p-GaP first current diffusion layer 326 (thickness: 1.5 μm, Zn doping: 1×1018 cm−3), an n-GaP current blocking layer 327 (thickness: 0.4 μm, Si doping: 3×1018 cm−3), and a p-GaP second current blocking layer 328 (thickness: 6 μm, Zn doping: 2×1018 cm−3) are grown on an n-GaAs substrate 330 by MOCVD process, and a first electrode 331 is formed on the substrate side while a second electrode 332 is formed on the grown layer side.
In this semiconductor light-emitting device, the n-GaP current blocking layer 327 is subjected to etching removal with its device center region left, and the second current diffusion layer 328 is re-grown thereon.
In this semiconductor light-emitting device, as shown in FIG. 26C, a current injected from the grown-layer side second electrode 332, avoiding the n-GaP current blocking layer 327 provided under the second electrode 332, flows to both sides of the n-GaP current blocking layer 327. As a result, as compared with the semiconductor light-emitting device shown in FIG. 25, this semiconductor light-emitting device involves less ineffective current that flows to under the second electrode 332, resulting in increased emission intensity. With this semiconductor light-emitting device applied to a 5 mm dia. molded article, the emission intensity at a 20 mA current conduction was 2.0 cd, an increase of slightly more than 30% as compared with the semiconductor light-emitting device shown in FIG. 25. However, because the thickness of the p-GaP first current diffusion layer 326 provided under the n-GaP current blocking layer 327 is as thick as 1.5 μm, there is still a sneak current going to under the n-GaP current blocking layer 327 as shown in FIG. 26C. Thus, there is a problem that the ineffective current is not eliminated completely.